/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.result.method.annotation;

import java.util.Collections;
import java.util.List;
import java.util.Map;

import org.springframework.core.MethodParameter;
import org.springframework.core.ReactiveAdapterRegistry;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;
import org.springframework.util.Assert;
import org.springframework.util.CollectionUtils;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.util.StringUtils;
import org.springframework.web.bind.annotation.MatrixVariable;
import org.springframework.web.bind.annotation.ValueConstants;
import org.springframework.web.reactive.BindingContext;
import org.springframework.web.reactive.HandlerMapping;
import org.springframework.web.reactive.result.method.HandlerMethodArgumentResolverSupport;
import org.springframework.web.reactive.result.method.SyncHandlerMethodArgumentResolver;
import org.springframework.web.server.ServerWebExchange;

/**
 * Resolves arguments of type {@link Map} annotated with {@link MatrixVariable @MatrixVariable}
 * where the annotation does not specify a name. In other words the purpose of this resolver
 * is to provide access to multiple matrix variables, either all or associated with a specific
 * path variable.
 *
 * <p>When a name is specified, an argument of type Map is considered to be a single attribute
 * with a Map value, and is resolved by {@link MatrixVariableMethodArgumentResolver} instead.
 *
 * @author Rossen Stoyanchev
 * @see MatrixVariableMethodArgumentResolver
 * @since 5.0.1
 */
public class MatrixVariableMapMethodArgumentResolver extends HandlerMethodArgumentResolverSupport
        implements SyncHandlerMethodArgumentResolver {

    public MatrixVariableMapMethodArgumentResolver(ReactiveAdapterRegistry registry) {
        super(registry);
    }


    @Override
    public boolean supportsParameter(MethodParameter parameter) {
        return checkAnnotatedParamNoReactiveWrapper(parameter, MatrixVariable.class,
                (ann, type) -> (Map.class.isAssignableFrom(type) && !StringUtils.hasText(ann.name())));
    }

    @Nullable
    @Override
    public Object resolveArgumentValue(MethodParameter parameter, BindingContext bindingContext,
            ServerWebExchange exchange) {

        Map<String, MultiValueMap<String, String>> matrixVariables =
                exchange.getAttribute(HandlerMapping.MATRIX_VARIABLES_ATTRIBUTE);

        if (CollectionUtils.isEmpty(matrixVariables)) {
            return Collections.emptyMap();
        }

        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
        MatrixVariable annotation = parameter.getParameterAnnotation(MatrixVariable.class);
        Assert.state(annotation != null, "No MatrixVariable annotation");
        String pathVariable = annotation.pathVar();

        if (!pathVariable.equals(ValueConstants.DEFAULT_NONE)) {
            MultiValueMap<String, String> mapForPathVariable = matrixVariables.get(pathVariable);
            if (mapForPathVariable == null) {
                return Collections.emptyMap();
            }
            map.putAll(mapForPathVariable);
        } else {
            for (MultiValueMap<String, String> vars : matrixVariables.values()) {
                for (String name : vars.keySet()) {
                    for (String value : vars.get(name)) {
                        map.add(name, value);
                    }
                }
            }
        }

        return (isSingleValueMap(parameter) ? map.toSingleValueMap() : map);
    }

    private boolean isSingleValueMap(MethodParameter parameter) {
        if (!MultiValueMap.class.isAssignableFrom(parameter.getParameterType())) {
            ResolvableType[] genericTypes = ResolvableType.forMethodParameter(parameter).getGenerics();
            if (genericTypes.length == 2) {
                Class<?> declaredClass = genericTypes[1].getRawClass();
                return (declaredClass == null || !List.class.isAssignableFrom(declaredClass));
            }
        }
        return false;
    }

}
